The present invention relates to an improved valve which when subjected to fire or elevated temperatures which will destroy the stem packing will react to such temperatures prior to the destruction of the stem packing to move to its fail safe position and to back seat to prevent any loss of fluid from the valve chamber when the packing is destroyed.
Prior to the present invention, there have been numerous valves of this type which included a fusible material in supporting relationship to the position of the stem so that when a fire melted the fusible material, it allowed the stem to move to its safe position with the stem shoulder engaging the seat surrounding the outer portion of the stem which is above the shoulder. This back seating prevented fluids within the valve chamber below the seat from flowing past the destroyed packing and feeding the fire. It is also desired that the stem move to its backseated position before the fire causes the building of excessive pressure in the valve chamber.
U.S. Pat. No. 4,214,600 discloses such a valve in which the heat sensitive material is within the cap surrounding the outer end of the stem. It operates to release support for the stem whenever it is subjected to a level of heat at which it melts which allows the stem shoulder to engage the seat surrounding the bonnet opening through which the stem extends. This prevents the passage of fluids within the valve from being discharged through the area in which the stem packing is contained.
U.S. Pat. No. 4,245,661 discloses another similar structure supported by fusible material which when it melts allows the stem to back seat and prevent the discharge of fluids contained within the valve through the stem passage.
U.S. Pat. No. 4,570,659 discloses another valve which utilizes eutectic material to support the valve stem to prevent back seating until the material melts.
U.S. Pat. No. 4,540,013 discloses a fire responsive stem retention apparatus which includes securing the inner cap to the outer sleeve by sweating it thereon with fusible material. This is used to prevent axial movement of the stem and to allow the stem to move and backseat when the fusible material melts and releases the inner cap and allows backseating of the stem.
Thus, U.S. Pat. Nos. 4,214,600; 4,245,661; 4,540,013; and 4,570,659 all disclose valves which include a fusible material to prevent the valve from backseating during normal operations but which melts to allow the valve to back seat when exposed to fire or excessive heat. However, none of these patents has recognized the problem of a fire heating the body of the valve away from the fusible material which can cause the stem packing to fail before the fusible material melts and allows backseating.
It has been discovered that if the fire is directed at the body of the valve and the fusible material is contained within the bonnet, the fusible material may not melt and release its support of the stem before the stem seals or packing are destroyed so that the valve leaks past the stem which renders it useless and dangerous.
Prior to the present invention, the use of heat pipes has been known. Such heat pipes are efficient heat transfer devices which functions to transfer heat to attempt to keep both ends at the same temperature. An article on heat pipes appeared, entitled "The Heat Pipe: Hot New Way to Save Energy" in the Mar. 11, 1976 issue of Machine Design, pages 52 to 56. Heat Pipes are available from Thermacore, Inc. of Lancaster, Pa.